Salt-dependent regulation of chloride channel transcripts in rice

Rice OsCLC1 homologous to voltage-dependent Cl− channels of the CLC-family was characterized to study the regulation of Cl− homeostasis under salt stress conditions. By transcript analyses, expression of OsCLC1 was found in leaves and roots. Transcriptional regulation during salt stress was compared in the salt-sensitive Cl−-accumulating rice line IR29 and the salt-tolerant Cl−-excluding rice line Pokkali. In response to salt stress OsCLC1 transcript levels were repressed in leaves and roots of IR29 whereas in Pokkali expression was transiently induced. Under same conditions, in IR29 mRNA levels of the Na+/H+ antiporter OsNHX1 and of the vacuolar H+-ATPase subunit OsVHA-B decreased upon salt stress whereas Pokkali showed transient stimulation of OsVHA-B transcripts. Cell-specificity of OsCLC1 transcription was analyzed by in situ PCR. In leaves, signals were detected in mesophyll cells and stomata. In addition, expression occurred in xylem parenchyma cells and in the phloem whereas in salt-treated plants transcript amounts were reduced in mesophyll cells. Our results indicate coordinated regulation of anion and cation homeostasis in salt-treated rice and suggest function of OsCLC1 in osmotic adjustment at high salinity.